1. Field of the Invention
The present invention relates to an image display method in a transmissive-type liquid crystal display device and to the transmissive-type liquid crystal display device and more particularly to the image display method in the transmissive-type liquid crystal display device to display an image made up of a moving picture and a still picture on a transmissive-type liquid crystal display (LCD) and to the transmissive-type liquid crystal display device employing the above image display method.
The present application claims priority of Japanese Patent Application No. 2001-126686 filed on Apr. 24, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
One example of an image made up of a moving picture and a still picture is a television picture. There are various types of methods of transmitting a television image and in the case of, for example, NTSC (National Television System Committee) method, a period (frame period) during which a television picture is displayed on a display screen, for example, a CRT (Cathode Ray Tube) is 16.7 ms. In an LCD, time (response time) required for switching between one screen and another screen is 20 ms to 30 ms, due to its characteristics, which is longer than the frame period of 16.7 ms described above. The response time becomes longest when a display is switched from a black to a white or from a white to a black on an LCD. Therefore, a display characteristic obtained when a television picture is displayed on the LCD is inferior to that obtained when the television picture is displayed on the CRT display screen. To solve this problem, when the image made up of the moving picture and the still picture such as the television picture or a like is displayed on the LCD, various technologies are conventionally proposed with an aim of achieving the display characteristic being equal to the display characteristic that the CRT display can provide. For example, Japanese Patent Application Laid-open No. Sho 64-82019 discloses a liquid crystal display device that can display a sharp picture having a high contrast ratio. The disclosed liquid crystal display device includes an illuminating section having a plurality of light-emitting portions each being able to selectively flash as a backlight of the LCD and an illuminating and scanning section. adapted to sequentially scan and flash each of the light-emitting portions with timing when a scanning electrode making up the LCD is driven. The illuminating and scanning section controls so as to turn on each of the light-emitting portions immediately after all scanning electrodes existing in a corresponding range where illuminating is needed have been selected and to turn off the light-emitting portions after a specified period of time. Hereinafter, the technology employed in this disclosed liquid crystal display device is called a “first conventional example”.
Moreover, Japanese Patent Application Laid-open No. Hei 11-109921 discloses a liquid crystal display device which displays a moving picture having less blur and having high quality and having no ghosting on an LCD. In the disclosed liquid crystal display device, a scanning electrode making up the LCD is selected to display an image on the LCD during one period out of frame periods during which an image is displayed and, at the same time, an image signal to display the above image is fed to a data electrode making up the LCD. Next, in the liquid crystal display device, the above scanning electrode is selected again during a period being different from the above one period out of the same frame periods that contains the above one period and a non-image signal (a so-called “blanking signal”) having a specified potential and being different from the above image signal is fed to the above data electrode. Hereinafter, the technology employed in this disclosed liquid crystal display device is called a “second conventional example”.
In the liquid crystal display device of the above first and second conventional examples, irrespective of whether an image to be displayed on the LCD is a moving picture or a still picture, the LCD and illuminating section are controlled by a same way which provides ease of control. Therefore, in the first conventional example, there is conventionally a shortcoming that a display screen flickers. Moreover, in the first conventional example, if the backlight is turned on, for example, only for a period being one-fourth of one frame period, in order to maintain same display luminance as is in a case where the backlight is turned on all the time, fourfold display luminance is required when being estimated by using a simplified calculation. This presents a problem in that power consumption by the backlight is large. This, therefore, causes a scale of a power supply circuit for supplying power to the backlight to become large and the power supply circuit to be high-priced.
On the other hand, in the second conventional example, there are shortcomings in that, when a moving picture is displayed in the LCD, a phenomenon called a “trail-leaving phenomenon (trail-effect)” occurs in which a trail-like unwanted image is left after a moving object in an image on a screen and/or a phenomenon called an “image-retention phenomenon” occurs in which an image that was previously displayed is still left on a screen. Moreover, in the second conventional example, if an image signal is supplied for a period being one-fourth of one frame period to a data electrode of the LCD, to maintain same display luminance as is in a case where an image signal is fed for all the periods of one frame period, fourfold display luminance is required when being estimated by using a simplified calculation. This causes power consumption by the backlight to become large.